1. Intro to Endocrine System Flashcards
what is the endocrine system?
a system of ductless glands which secrete chemical messengers into the blood
general action of a hormone
released from endocrine gland and carried in blood to act on cells with correct receptors
pituitary gland
situated below brain
sometimes called ‘master gland’
thyroid and parathyroid glands
situated in neck
important for control of metabolic rate and calcium homeostasis §
pancreas
secretes insulin into blood regulates blood glucose concentrations and utilisation
adrenal glands
on top of kidneys
divided into outer cortex and inner medulla
gonads
secrete female and male reproductive hormones
responsible for development of secondary sexual characteristics
mechanisms of hormone action
steroid hormone receptors
g-protein coupled receptors
tyrosine kinase receptors
how do steroid hormone receptors work?
hormone crosses cell membrane to bind to receptor (cytoplasmic or nuclear)
hormone receptor complex binds to hormone-response element of DNA - influences gene transcription
receptor may be constitutively active
how do g-protein coupled receptors work?
hormone binds to 7TM receptor, causing synthesis of second messenger
second messengers phosphorylate intracellular, regulatory proteins which influence cell activity, eg smooth muscle contraction
how do tyrosine kinase receptors work?
membrane-bound enzyme is single strand of protein
often, 2 receptors must be present for action to work
hormone molecule binds to each receptor
receptor acts as enzyme to phosphorylate tyrosine components of intracellular regulatory proteins
characteristics of peptide hormones
chains of amino acids
highly water soluble
susceptible to protease attack = not orally active
unable to cross cell membrane without carrier protein
act on membrane-bound receptors
rapid onset of action
short plasma life and duration of action
characteristics of steroid and thyroid hormones
highly lipid soluble, poorly water soluble
transported in blood bound to plasma protein
can cross membrane to act on intracellular receptors
slow onset of action
long plasma half life and duration of action
what is a stimulating (trophic) hormone?
secretion of hormone by a given gland is controlled by the anterior pituitary gland
how is thyroxine released?
hypothalamus secretes thyrotrophin releasing hormone (TRH)
TRH acts on ant pituitary gland: releases TSH
TSH acts on thyroid gland, stimulating secretion of thyroxine
